MAX1501
Highly Integrated, Linear Battery Charger with
Thermal Regulation for Portable Applications
12 Maxim Integrated
to set the regulation voltage to 4.95V to not interfere with
µP charge control. When the regulation voltage is 4.95V,
VIN must be ≥5.25V.
The MAX1501 precharges with 10% of the user-pro-
grammed charge current at the start of a charge cycle.
Fast charge begins when VBATT exceeds 2.8V. A resis-
tor from SETI to GND sets charge current. See the
Charge-Current Selection
section. The MAX1501 enters
voltage mode and decreases charge current when
VBATT reaches 4.5V.
The thermal-regulation loop limits die temperature to the
value selected by TEMP by reducing charge current. See
the
Thermal-Regulation Selection
section. This protects
the MAX1501 from overheating when supplying high
charge currents, or operating from high input voltages.
Set the top-off-current threshold with the three-state
FULLI input. See the
Top-Off-Current Selection
section.
RLED goes high impedance and GLED asserts low
when the top-off current threshold is reached. The
MAX1501 automatically initiates recharging when the
battery voltage drops below 4V. The MAX1501Z does
not time out.
No-Battery Mode
Connect CHGEN and MODE to VL to place the MAX1501
in no-battery mode. An external load can be connected to
BATT in this mode. VBATT regulates to 4V in no-battery
mode, regardless of the state of SELV.
The current-control loop, voltage-control loop, and
thermal-control loop all function in no-battery mode.
The loop gain of the voltage-control loop decreases to
ensure stability with no battery present. Connect a 10µF
ceramic capacitor to BATT for stability. RLED and
GLED are both high impedance in no-battery mode.
ACOK
The ACOK output asserts low when VIN is present, 4.2V
≤VIN ≤6.25V, and VIN - VBATT > 100mV. The ACOK
open-drain output requires an external 100kΩpullup
resistor to an external supply voltage. The external
supply voltage must be less than 5.5V.
RLED
and
GLED
Indicators
RLED and GLED serve as visual indicators that power
is applied as well as the charge status of a battery.
RLED asserts low when a wall adapter is connected
and a battery is charging, regardless of cell chemistry.
GLED asserts low when power is applied and the bat-
tery is fully charged. Both outputs go high-impedance
in shutdown. Connect the anode of each LED to IN,
and the cathode to RLED or GLED. Table 3 summa-
rizes the behavior of RLED and GLED under normal
operating conditions. Connect pullup resistors to the µP
I/O supply when interfacing RLED and GLED with a
µP’s logic inputs.
Soft-Start
A ten-step, soft-start algorithm activates when entering
fast-charge mode. The charging current ramps up in
10% increments, 20ms per step, to the full charging
current when VBATT exceeds 2.8V.
Applications Information
Charge-Current Selection
Program the charging current using an external resistor
between SETI and GND. Set the charge-current resistor
with the following equation:
If VSETI = 1.4V, the current-control loop controls the
battery charging. If VSETI < 1.4V, either the voltage-
control loop or the thermal-control loop operates.
Measure the charging current by monitoring VSETI and
using the following equation:
.